A cellular wireless access network typically includes a number of base stations that are configured to provide wireless coverage areas, such as cells and cell sectors, in which user equipment devices (UEs) such as cell phones, tablet computers, machine-type-communication devices, tracking devices, embedded wireless modules, and/or other wirelessly equipped communication devices (whether or not user operated), can operate. Each base station could be coupled with a core network including a gateway system that provides connectivity with various application servers and/or transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the access network could engage in air interface communication with a base station and could thereby communicate via the base station with various application servers and other entities.
Such an access network could operate in accordance with a particular air interface protocol (or radio access technology), with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link.
In accordance with the air-interface protocol, each coverage area could operate on one or more carriers, each of which could be frequency division duplex (FDD), defining separate frequency channels for downlink and uplink communication, or time division duplex (TDD), with a single frequency channel multiplexed over time between downlink and uplink use. Further, on the downlink and uplink, each such carrier could be structured to define various physical channels for carrying information between the base stations and UEs.
Over the years, the industry has embraced various “generations” of air-interface protocols, in a continuous effort to increase available data rate and quality of service for end users. These generations have ranged from “1G,” which used simple analog frequency modulation to facilitate basic voice-call service, to “4G”—such as Long Term Evolution (LTE), which now facilitates mobile broadband service using technologies such as orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO). And most recently, the industry is now exploring developments in “5G” and particularly “5G NR” (5G New Radio), which may use a scalable OFDM air interface, advanced channel coding, massive MIMO, beamforming, and/or other features, to support higher data rates and countless applications, such as mission-critical services, enhanced mobile broadband, and massive Internet of Things (IoT).
When a UE first enters into coverage of such an access network, the UE could detect coverage of a base station and then engage in random-access signaling and connection signaling with the base station in order to establish an air-interface connection (e.g., Radio Resource Control (RRC) connection) defining a logical tunnel for carrying communications wirelessly between the UE and the base station. Further, the UE could engage in attachment signaling via the base station with a control system of the access network. And the control system could responsively authenticate the UE and then engage in signaling to set up for the UE one or more default bearers defining logical tunnels for carrying data between the UE and the gateway system, to facilitate UE communication on one or more transport networks.
To facilitate voice over Internet Protocol (VoIP) service and other packet-based real-time communication services, an access network like this could provide connectivity with an Internet Multimedia Subsystem (IMS), which could include a call server and other components for setting up and connecting packet-based real-time media sessions for UEs. For instance, the gateway system of the access network could have a packet-switched communication interface with the IMS, so that a UE served by a base station can engage in packet-based communication with the IMS via the UE's established air-interface connection and a default bearer, and via the interface between the gateway system and the IMS. Further, the control system of the access network could have a packet-switched communication interface with the IMS, to allow for control signaling between the IMS and the access network.
In order to set up a packet-based real-time media session between the UE and a remote party via the IMS when the UE places a VoIP call or the like, the UE could engage in packet-based session-setup signaling, such as Session Initiation Protocol (SIP) signaling, with the IMS via the UE's air-interface connection and a default bearer through the access network, and the IMS could responsively engage in corresponding session-setup signaling with the remote party. Through this session-setup signaling, a packet-based real-time media session could thereby be established between the UE and the remote party, typically bridged through the IMS.
Further, to help ensure that content of the media session gets transmitted through the access network with an appropriate level of quality as it passes between the UE and the remote party, the IMS could engage in signaling with the access network, to arrange for the access network to set up a dedicated bearer for carrying content of the media session.
For example, the IMS could transmit to the control system of the access network a bearer-setup request message that identifies the UE (per the UE's session-setup signaling) and indicates a required bit rate, and the control system could then responsively work with the gateway system to invoke setup of a dedicated bearer supporting that bit rate (i.e., a guaranteed bit rate bearer) and other quality parameters. In response, further signaling could then pass between the components of the access network, ultimately resulting in creation of the dedicated bearer for the UE. And as part of this process, the base station could reserve appropriate resources to support the dedicated bearer.